Lancing devices are typically handheld units that permit users to draw blood for testing and diagnostic purposes. These devices include a housing with a piercing aperture, a lancet that contains one or more needles, and a firing mechanism. The firing mechanism typically includes a spring or other biasing means which can be cocked either by insertion of the lancet or by pulling a cocking handle, for example. Once the lancing device is cocked, it is placed against the user's skin, often the fingertip. The user can then press a trigger to actuate the firing mechanism, which momentarily drives the sharp tip of the needle through the piercing aperture to puncture the user's skin and draw blood. When the lancing operation is complete, the user can press a second actuator to eject the lancet for removal and disposal.
A consideration in the design of lancets is to minimize the discomfort experienced by users during the lancing process. To this end, some lancing devices include mechanisms to adjust the distance that the needle sharp protrudes through the piercing aperture, thus regulating the depth that the needle penetrates the user's skin. In some cases, these depth adjustment mechanisms include adjustable stops that limit the forward movement of the lancet during firing. In other cases, depth adjustment mechanisms adjust the tip of the lancing device to reduce or increase the distance that the needle sharp protrudes from the lancing device. One approach for depth adjustment is illustrated in U.S. Pat. No. 5,984,940. A lancet holder is moved axially within a lancing device housing to move the needle closer to or farther away from the piercing aperture, thus adjusting penetration depth.
Another consideration in the design of lancing devices is to avoid accidental needle pricks when inserting and removing lancets from the lancing device. To this end, lancets include safety features such as frangible tabs which cover the needle sharp prior to insertion in the lancing device. Once the lancet is inserted, the use can break off and remove the frangible tab. Some lancets also include sleeves coaxially mounted to the main body of the lancet. The sleeve can be positioned so that it protectively encloses the needle sharp. During the lancing operation, the main body of the lancet slides through the sleeve to expose the lancet sharp. After removal of the lancet, however, the sleeve can be locked in its protective position, reducing the likelihood that a person handling the use lancet will prick himself or herself.
Lancing devices can draw blood from a user's fingertip or other body part. A fingertip is a good testing site because it contains a large number of blood vessels and it is therefore easy to draw an adequate quantity of blood from the fingertip. However, fingertips are also sensitive and users who must frequently draw blood samples may experience discomfort from repeated sampling of the fingertips. Therefore, some users also perform lancing operations on parts of the body, and this is known as alternate site testing or alternate site incision, also known as “AST.”
To effectively draw blood from an alternate site, it is helpful to have the needle penetrate the skin more deeply. It is also helpful to have a relatively wide piercing aperture. A wider piercing aperture acts as an expression ring by allowing the skin to pucker into the aperture's opening and by compressing a wider area of skin around the incision. When skin protrudes through the aperture into the housing, it is also more deeply penetrated by the lancet.
A piercing aperture that is suitably wide for AST lancing may be too wide for finger testing. Thus, some lancing devices provide removable endcaps with different size piercing apertures. A user attaches one endcap (with a wider piercing aperture) when the lancing device is used for AST lancing; and a different endcap (with a more narrow piercing aperture) when the lancing device is used for fingertip lancing.
Another approach has been proposed in which the piercing aperture is adjustable in size, as illustrated in US Pat. Application 2004/0236251. The smaller size is used during the incision, whether on a fingertip or alternate site. Once the incision is made, the piercing aperture is expanded to provide a larger opening that can be used to express the desired quantity of blood from an alternate site. The size of the piercing aperture can be adjusted by moving a reference member into the piercing aperture, effectively obstructing the opening and providing a flat surface against which the user's skin (fingertip or alternate site) is pressed for lancing. After the incision is made, the reference member is retracted to provide an unobstructed, relatively wide expression opening.
It has also been proposed that the reference member be attached to the lancet itself. During incision, the lancet and the reference member are moved together toward the piercing aperture to effectively narrow the piercing aperture. After incision, the reference member and the lancet are retracted to leave the piercing aperture unobstructed. Prior to the lancet's insertion into the lancing device, the reference member can be adjusted relative to the lancet for purposes of regulating the penetration depth of the needle.
Another consideration in the design of lancing systems is the ease with which a lancet can be inserted into the lancing device. It is known that when a lancet is inserted into a lancing device, the force of the insertion can be used to cock the device. However, if the device is already cocked, and a lancet was to be inserted, there is some risk that the device would discharge during the insertion process and the user would be accidentally pricked. It is also known to provide a removable cap on the housing to permit insertion of the lancet. However, this requires an additional step in the process (namely, removing the cap). It would be desirable to provide a lancing device that can be loaded without removal of the cap and that could not be loaded when cocked.
Another consideration in the design of lancets is to minimize the handling of the lancet by the user during ejection of the lancet from the lancing device. To this end, it is known to provide ejection mechanisms that include a sliding member that engages the lancet to push it out of the lancing device. In such cases, it is helpful to restrain the lancet carrier from forward movement. Known mechanisms for achieving this use the sliding member to actuate a releasable connector to engage the lancet carrier and prevent its forward movement, as shown for example in U.S. Pat. No. 6,197,040. The releasable connector is biased towards the ejection slide and away from the lancet carrier and is configured so that when the lancet carrier is urged forward, a force vector is transmitted through the connector to the ejection slide. This means that the slide and the ejector rub against each other with a degree of force, causing friction that is discernible to the user. It would be desirable to provide an ejection mechanism that minimizes friction and force imposed on moving parts to reduce wear.